TITLE
Queueing models for large-scale service systems experiencing periods of overloading

ABSTRACT
Motivated by large-scale service systems, such as customer contact centers and hospitals, we have developed a deterministic fluid model and a stochastic refinement that approximate the many-server G_t/GI/s_t+GI queueing model, having a general arrival process with time-varying rate (the G_t), i.i.d. service times with a general distribution (the first GI), time varying staffing (the s_t) and customer abandonment from queue with i.i.d. patience times having a general distribution (the +GI). The analysis applies to a system that alternates between overloaded and underloaded intervals. With time-varying arrivals, such alternating behavior commonly occurs when it is difficult to dynamically adjust the staffing level in response to changes in demand. We have applied the fluid model to predict the delays of arriving customers.

Based on joint work with former doctoral students Yunan Liu, Guodong Pang and Rouba Ibrahim
Papers available at: http://www.columbia.edu/~ww2040/allpapers.html